Study On The Anisotropy Of Mechanical Properties Of Consecutive Point-mode Forging And Laser Rapid Forming TA15 Titanium Alloy

TA15 titanium alloy,corresponding to Russian grade BT20,which nominal composition is Ti-6.5Al-2Zr-1Mo-1V.TA15 titanium alloy was successfully developed by the former Soviet Union in 1964 as a medium strength near ? titanium alloy.Owing to it's medium room temperature and high temperature strength,good thermal stability and weldability,TA15 titanium alloy was widely used in the aerospace industry as the main material for manufacturing structural bearing parts.Laser Rapid Forming(LRF)parts,due to it's inherent process limitation,coarse columnar ?-grains with preferential orientation along the deposition direction has anisotropic mechanical properties.In such a case,application under complex multi-directional stress conditions was limited.In this paper,a TA15 thick-walled parts was manufactured by the Consecutive Point-Mode Forging and Laser Rapid Forming(CPF-LRF)technology,effect of heat treatment in the(?+?)phase field on microstructure and anisotropic mechanical properties was studied by using the OM and SEM,mechanical properties testing was followed.The effects of heat treatment regime on the microstructure of TA15 alloy and its evolution characteristic were studied.The difference in microstructure and mechanical properties perpendicular to the deposition height direction(H direction)and along the deposition height direction(V direction)was discussed,combined with analyzing of the fracture morphology of specimens.Possibility of solving the inherent defects of the laser Rapid Forming technology was explored.The results show that the TA15 alloy parts formed by CPF-LRF technology has good structural uniformity,and the microstructure has a uniform equiaxed grain morphology in horizontal direction and vertical direction;heated at the(?+?)phase region will cause the breaking of ? grain boundary,but as the annealing temperature or holding time increases,the ? grain boundary phase will coarsen.Annealed at higher temperature,with increases of the holding time,the equiaxed ? phase will growing;the results of uniaxial tension test at room temperature shows that the H-direction sample of TA15 alloy reaches the maximum elongation of 11.2% at 945 °C,and the sample of V-direction got it's best elongation rate of 13.1% at 925 °C.Therefore,below the priority ensuring sufficient strength of the material,the heat treatment region between 925 and 945 °C of the TA15 titanium alloy can reduce the anisotropy of mechanical properties and expanding the application range of the material on multidirectional stress condition.